Turbine wheel and blade construction



m 1955 A. T. COLWELL TURBINE WHEEL AND BLADE CONSTRUCTION 2 Sheets-Sheet1 Filed Aug. 24, 1946 INVENTOR.

ARCH/E 7'. CO1. WELL Jan. 18, 1955 A. 'r. COLWELL TURBINE WHEEL ANDBLADE CONSTRUCTION 2 Sheets-Sheet 2 Filed Aug. 24, 1946 INVENTOR AQcH/ET. COL WELL.

United States Patent TURBWE WHEEL AND BLADE CONSTRUCTION Archie T.Colwell, Cleveland, Ohio, assignor to Thompson Products, Inc.,Cleveland, Ohio, a corporation of Ohio Application August 24, 1946,Serial No. 692,762

10 Claims. (Cl. 253-3915) My invention relates to the coolingof rotatingdevices, such as, for example, the blades used in superchargers, etturbines, gas turbines, and the like.

The blades of gas turbines, superchargers, jet turbines, and the likeare subjected to very high temperatures by the working fluid, such asburning gases, acting thereagainst. While highest operating efliciencymay be obtained with the hottest working fluids, known blade metalscannot be heated to the temperature of such efiicient fluids withoutexcessive distortion, and early failure under the stresses imposedthereon. Therefore, the max mum temperature of the gas or other workingfluid acting upon the blades has heretofore been limited by the heatresistance properties of the blade metals.

According to this invention more efficient and hotter working fluids canbe used without damaging the blades by improving the heat dissipatingproperties of the blades especially along the radial lengths of theblades. This increases the temperature gradient at the surface of theblades and thus decreases the blade temperature as compared to thetemperature of the workmg fluid.

'It is an object of my invention to provide an improved rotating elementfor turbine blades, and the like, wherein more effective heat transferfrom the outermost portion to the innermost portion is obtained.

Another object of my invention is to provide an rmproved element for usein a rotating structure having good heat transfer in the radialdirection while at the same time avoiding the need for piping or otheradditional apparatus.

Also it is an object of my invention to provide an element for use inrotating structures having a high degree of heat transfer in the radialdirection and which is adapted for use in superchargers, jet turbines,gas turbines and the like.

Another object is to provide a hollow turbine bucket for jet engines andthe like.

Further it is an object of my invention to provide a coolant filledhollow turbine blade wherein centrifugal action inherent in therotational motion thereof acts to supplement the natural forces causingconvection currents in the coolant and hence improves the coolingaction.

Still another object of my invention is to provide an improved blade foruse in gas turbines and the like which is effective even though one sideof the blade tends to be heated to a greater extent than the other sidethereof.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings.

On the drawings:

Figure 1 is an elevational view of a gas turbine wheel and bladeassembly constructed in accordance with-the principles of my invention;

Figure 2 is an enlarged elevational view of a portion of the gas turbinewheel and blade assembly of Fig. 1, portions thereof being shown insection;

Figure 3 is an enlarged axial section of the blade and wheel structureof Figure 1;

Figure 4 is an axial section of an alternate embodiment of the structureof Figure 1;

Figure 5 is an alternate construction of the blade for use in thestructure of Figure 1; and

Patented Jan. 18, 1955 Figures 6 and 7 show still another embodiment ofthe blade for use in the structure of Figure 1.

As shown on the drawings:

Figure 1 shows the construction of a turbine wheel embodying thefeatures of my invention as viewed in the axial direction. Thisstructure consists of wheel portion, shown generally at 10, attached bybolts 26 to shaft 10a to rotate therewith and on which a plurality ofblades 11 are mounted. As shown more clearly in Figure 3, these bladeshave root ends with superimposed stepped notches 13 in the front andrear faces thereof to coact with similar notches in the two flanges 14and 15 constituting wheel 10. The blades 11 are securely fastened toflanges 14 and 15 by means of bolts 12 which are equally spaced aboutthe periphery of the wheel as shown in Figure 1.

In accordance with my invention blade 11 is hollow and has a recess 16therein, extending in the radial direction therethrough and varying insize in accordance with the blade structure so as to provide wallsthereof of sufficient thickness to support the stresses imposed by theforce of the gas impinging on the blade. This radially inner or root endof the recess is in communication with the interior of .a cooling bulb17. This bulb 17 is preferably constructed of copper and brazed into theroot end of the blade. The blade is composed of high heat alloy metaland copper is particularly suitable for the brazing metal because of itsgood thermal conductivity. The bulb l1317 lilepends radially from theinner or root end of the a e.

As will be described in further detail hereafter, the recess 16 isfilled with coolant C such as sodium to increase conduction of heat fromthe hot outer periphery to the cooler bulb 17 and thereby limit thetemperature of the blade 11 in the regions exposed to the hot blast ofthe working fluid.

Cooling of bulb 17 is preferably achieved by a blast of air or otherfluid thereacross. Figure 3 shows an axial cross-section of onestructure for supplying this cooling medium, this structure includingshield 18 which is arranged to guide cooling medium from a region ofsmall radius outwardly to the portion of the flanges 14 and 15immediately below the blade 11 and communicating with cooling bulb 17.At this point, the fluid passes across cooling bulb 17 and is dischargedin the axial direction. Ports 24 in flange 14 and ports 25 in flange 15are provided to register with the space between each pair of adjacentbulbs 17 to permit cooling fluid to flow over the bulb walls. TheseWalls are preferably corrugated to in crease the surface area thereof.Figure 2 shows a crosssectional view of the turbine wheel with theshield 18 removed. It will be observed that suflicient space is providedbetween adjacent cooling bulbs 17 to permit the flow of cooling mediumtherebetween.

till the operation of the above-described turbine wheel and bladeconstruction, the outwardly extending portions of blade 11 are exposedto the high temperature working fluid which in the case of aturbo-supercharger is the hot exhaust gas from the connectedreciprocating engine and in the case of a jet turbine is the heatedair-gas mixture constituting the working fluid. This fluid, in passingacross the outermost portion ofblade 11 (designated as 11-a in Figure 3)heats the blade 11. This causes heat flow through the blade walls to thecoolant C such as sodium contained therein, thus increasing thetemperature [thereof and causing liquefaction of the entire mass ofmaterial with-in the recess. Further, heat transfer due to the presenceof the hot gases flowing past the outer periphery of blade 11 causes thesodium at the outermost portion to become less dense and hence produce asmaller pressure due to centrifugal forces than would exist at lowertemperature. Inasmuch as the fluid pressure in all directions isidentical, this causes the heavier, lower temperature, sodium from theportions of the blade having smaller radius, to be forced outwardly andthe hotter, low density, sodium at the outermost portion of the blade tobe forced inwardly. Hence a fluid flow is set up as shown by the arrowsof Figure 3. When the fluid reaches bulb 17, the cooling air or otherfluid passing across the surface thereof tends to cause heat transfertherefrom. Since this heat must be taken from the fluid contained withinthe bulb 17, that fluid is cooled and becomes more dense, therebycausing increased pressure by reason of the centrifugal accelerationthereof and thus causing outward flow toward the extended portion 11a ofthe blade.

The rate of circulation of the sodium contained within the recess 16 andcooling bulb 17 is very great by reason of the large centrifugal forcesassociated with rotation of the turbine Wheel as compared with thecirculation that would be achieved in the presence of gravity alone. Inthis respect, the direction of flow of the cooling medium is contrary tothe direction that would be anticipated inasmuch as the fluid containedin the portions having maximum radial distance and hence greatestcentrifugal force are forced inwardly against the centrifugalacceleration to cooling bulb 17. As is well known, this rapid fluid flownot only causes the heat to be transferred from the outermost portion ofthe blade 11 to the innermost portion of bulb 17 at a rapid rate butalso, by reason of the relative motion against the inner surfaces ofrecess 16 and bulb 17, improves the heat transfer therebetween so thatan eflicient and effective cooling action is obtained. Inasmuch as thiscooling action tends to cause the bulb portion 17 to assume thetemperature of the outer portion 11a of blade 11, the cooling mediumpassing by bulb 17 is exposed to a surface having relatively hightemperature. Since the amount of heat energy passed from the surface ofbulb 17 to the cooling medium is dependent on the temperature differencetherebetween, this relatively high temperature of the cooling bulb 17thus increases the rate of heat transfer to the cooling fluid, therebyincreasing the rate of heat transfer from the blade portion 11-a to thecooling fluid. As is well known, the increased rate of heat transfercauses a corresponding increased temperature gradient between theworking fluid to which blade 11a is exposed and the blade itself,thereby reducing the blade temperature relative to the temperature ofthe working fluid and enabling a greater temperature of the latterwithout causing undesired weakening, creep, or fatigue of the bladematerial.

Figure 4 shows an alternative embodiment of a turbine wheel and bladeconstructed in accordance with our invention. As shown in this figure,the flange 14a is made solid and cooling air applied to bulb 17 throughthe annular opening between this flange and flange 15 which has anopening 25 suitable for passage of cooling air.

A further alternative blade construction is shown in Figure 5. In thisconstruction the root end of the blade, shown generally at 19, isextended radially inward to provide an integral portion for taking theplace of bulb 17. This portion has spaced parallel grooves 20 along theside faces thereof to provide fins therebetween which will be exposed tothe air passing through the ports 24 and 25 of the wheel. These groovesmay be milled along the surface of the lower end of the blade, a machineoperation that can readily be conducted in the mass production of theblade, thereby achieving minimum manufacturing costs thereof. Theincreased surface area exposed to the cooling medium by reason of thegrooves or slots 20 causes a corresponding increased heat transferthereto and thus enables the innermost portion of the blade to transferconsiderable heat notwithstanding the fact that it cannot easily beconstructed of high heat conductivity material such as the copper ofcooling bulb 17.

igures 6 and 7 show a further alternative construction of the blade 11intended for use where the flow of the working fluid past one side ofthe blade tends to cause greater heat transfer thereto than the otherside. In this construction, baflle 21 extends along the length of theblade to separate the portions of the blade tending to heat to thegreatest degree from the other portions thereof. An opening is providedbetween the top of baflle 21 and the most extended portion of blade 11and between the bottom of baffle 21 and the lowermost portion of coolingbulb 17 so as to provide a continuous passageway for the cooling mediumas shown in Figure 6. Figure 7 shows the structure of baffle 21 andblade 11 as seen from cross-section VII-Vli, Figure 6. As will beevident from Figure 7, the baflle extends entirely across the bladestructure so as to provide two distinct passageways in the radialdirection, one for outward flow of sodium and the other for inward flowthereof.

In the operation of the embodiment of my invention shown in Figure 6,one side of the blade 11, say, the left side as seen in Figure 6, tendsto have greatest heat, transferred thereto, as, for example, by reasonof the direction of flow of the working fluid. This heat causes thesodium or other medium contained therein to increase in temperature,thereby becoming less dense and being forced inwardly by reason of thegreater centrifugal pressure exerted by the more dense fluid in theother portion of the blade. This produces a continuous circulation offluid in the counterclockwise direction as seen in Figure 6, therebyproviding effective cooling action. In the embodiment of my inventionshown in Figures 6 and 7, it will be observed that the fluid flows in acontinuous path without eddy currents or other influences tending toincrease the fiuid friction and hence decrease the rate of flow, thusproviding a maximum degree of cooling action.

Figures 3 and 4 show one. method of constructing blade 11. In accordancewith this method, a suitable opening is provided in the lower portion ofcooling bulb 17, this opening being designated as 22 in the figures. Inthe manufacture of the blade, metallic sodium is passed through thisopening into the blade until the level of the sodium is such that only asmall air space is left therein, this space being only sufficient toaccommodate the increased volume of the sodium as the temperature israised. The opening 22 may then be closed by welding a plug thereto,thus sealing the unit for operation. In the blade of Figure 6, theopening 23 is provided in the end of blade 11 and the plug Weldedthereto after filling the recess 16 with sodium.

It will be observed that I have provided a self-contained hollow turbineblade having inherently good cooling properties when operating andtaking advantage of the centrifugal acceleration incident to turbineoperation. Furthermore, the spent cooling fluid is passed in an axialdirection from the wheel and may conveniently be combined with theexhaust Working fluid to be ejected from the unit. This is, in markedcontrast to previous attempts to cool turbine blades by means of acooling fluid as such attempts have required extensive piping systemsand have entailed considerable energy losses in the required pumping.

A further feature of the blade structure of Figures 1, 2 and 3 and themodification of Figure 4 resides in the fact that the functions ofcooling and blade operation are separated, the former function beingconfined to the cooling bulb 17 and the latter being confined to theblade portion 11. Thus, blade portion 11 may be constructed of materialhaving a high degree of resistance to creep, fatigue, and weakening atthe high temperatures induced by the exposure to the working fluidwhereas cooling bulb 17 may be made of copper or other material havinggood thermal conductivity but poor mechanical characteristics at thehigh temperatures of the blade portion 11.

The recess 16 provided in the turbine blades has only slight effect onthe ability thereof to withstand the forces associated with turbineoperation. As is well known, the blades act as cantilever beams incommunicating the force of the working fluid to the wheel and thematerial close to the neutral axis thereof provides little strength.Thus, the recess 16, located in the inner portions of the blade, reducesthe strength thereof to only a minor degree.

While I have described my invention with particular reference to a gasturbine such as might be used in a turbo-supercharger, it will beunderstood that its applications are not limited thereto and that it maybe applied to all elements mounted on rotating structures which tend tobe heated at their outer portions and it is desired to remove this heatby means of a heat flow from their inner portions.

It will, of course, be obvious to those skilled in the art that materialother than sodium may be contained within the recess 16 of the turbineblade, the principal requirements for such material being that it havesubstantial decrease in density with temperature and good heatconduction characteristics.

While I have shown particular embodiments of my invention, it will, ofcourse, be understood that I do not wish to be limited thereto as manymodifications both in the elements employed and their cooperativestructure may be made without departing from the spirit and scope of myinvention. I, of course, contemplate by the appended claims to cover anysuch modifications as fall within the true spirit and scope thereof.

I claim as my invention:

1. A turbine comprising in combination, a wheel including two axiallyspaced flanges, a blade having a hollow working portion extendingradially outside of said flanges to contact a high temperature workingfluid to develop turbine operating force, said blade having a fasteningportion between said flanges for cooperation therewith to rigidlymaintain said blade in position in said turbine wheel, said blade havinga hollow heat-transfer bulb portion extending radially inwardly fromsaid fastening portion into a hollow air space between said flanges,said flanges being slit at intervals to allow axial passage of air intosaid hollow air space, means for supplying air at a positive pressure tosaid slits, said bulb portion comprising a material having an extremelyhigh thermal conductivity, while said blade comprises a metal havinggreat heat resistance, and a fluid medium within said bulb and saidblade, said medium having a decreasing density with increase intemperature whereby operation of the turbine blade in high temperatureworking fluids will cause a convective current in the cooling mediumfrom the working portion of the blade to the bulb due to density changeswhich cause movement due to the action of centrifugal force.

2. A turbine comprising in combination, a wheel including two axiallyspaced flanges, a blade having a working portion and a root portion,said root portion including blade anchoring means in operativeengagement with the outer peripheries of said flanges, and said workingportion extending radially outwardly from said root portion and saidflanges to contact a high temperature working fluid to develop turbineoperating force, said blade having a hollow extension portion extendingradially inwardly from said root portion into the space between saidflanges, said working portion having a recess therein communicatingthrough said root portion with the hollow interior of said extensionportion and defining therewith a closed cavity within the blade, atleast one of said flanges having holes for the escape of fluid from theregion about said extension portion, and means to introduce coolingfluid between said flanges to cause escape thereof through said holes tocool said extension portion of said blade, and a fluid medium havingdecreasing density with increase in temperature at the temperature ofnormal operation contained within said recess and said extensionportion, thus to set up fluid flow tending to transfer heat from saidworking portion to said extension portion.

3. A turbine according to claim 2 wherein said blade extension portionis provided with external fins.

4. In a turbine rotor and blade assembly including a rotatable turbinewheel having a periphery for anchoring the roots of blades and a passageradially inward from said periphery for flow of cooling fluidtherethrough, the improvement of a blade having a root portion anchoredin said periphery of the turbine wheel, a vane portion extendingradially outward from the periphery of said turbine wheel and a coolingbulb portion extending radially inward from said root portion acrosssaid passage of the turbine wheel, said vane portion adapted to beexposed to high temperature working fluid for producing operating forcesto rotate said wheel, said cooling bulb being exposed to cooling fluidin said passage of the turbine wheel, said vane portion beingconstructed of high temperature resisting material, said bulb portionbeing constructed of high thermal conductivity material, said vaneportion having a recess therein communicating with the interior of saidcooling bulb, and a fluid medium having decreased density with increasedtemperature in the normal range of operating temperatures containedwithin the recess whereby rotation of the turbine wheel together withthe heating of the vane portion of the blade by the working fluid setsup fluid flow in said recess causing a transfer of heat from the vaneportion to said cooling bulb and a transfer of heat from the coolingbulb to a cooling fluid in said passage of the turbine wheel.

5. A turbine comprising in combination a wheel having a peripheral rimand a hollow air space inwardly from said rim, means for circulatingcooling air through said air space, a blade having a working vaneportion extending radially outward from said rim of said wheel, ananchoring root portion anchored in said rim of the wheel and a bulbportion extending radially inward from said rim across said hollow airspace, said working vane portion of the blade adapted to contact a hightemperature working fluid to develop turbine operating force forrotating said wheel, said blade having a cavity extending from the bulbportio'n through the vane portion, a fluid medium having decreaseddensity with increased temperature at the temperature of normaloperation of said blade contained within said cavity, and. means todirect a stream of cooling air through said hollow air space and aroundthe bulb portion to reduce the temperature of the bulb portion wherebyheating of said, fluid medium in the vane portion of the blade willdecrease the density of the medium in the vane portion and wherebyrotation of the wheel will create a centrifugal force transferring theheavier fluid medium from the bulb portion to displace the heated fluidmedium of decreased density in the vane portion and whereby the coolingfluid will cool the bulb portion to decrease the temperature of theheated fluid medium in the bulb thereby increasing its density andsetting up fluid flow transferring heat from the vane portion to preventoverheating of the vane portion by the working of fluid.

6. In a turbine wheel having a rim portion, a cooling space inwardlyfrom said rim portion and means for circulating cooling air through saidspace, the improvement of a hollow turbine blade having a vane portionextending radially outward from the rim portion of the wheel, a rootportion anchored in the rim portion of the wheel and a cooling bulbportion extending into the cooling space -to be cooled by air flowedtherethrough, a fluid medium in said blade having decreased density withincreased temperature, a bafile in the vane portion of said bladedividing the vane cavity into two communicating compartments including acompartment on one side of the baflle tending to be heated by theworking fluid for driving the turbine to a greater degree than thecompartment on the other side of the baffie whereby fluid currents areset up in,said blade along the length of the blade by the change indensity of the cooling medium as it is heated and by the centrifugalforces associated with rotation of the turbine to effect heat transferfrom the vane portion to the bulb portion, and said cooling air in thecooling space being effective to dissipate heat from the bulb portion.

7. In a turbine wheel assembly including a wheel having blade anchoringmeans around the periphery thereof and a cooling space inwardly from theperiphery, the improvement of a hollow turbine blade having a workingvane portion extending radially outward from the periphery of the wheel,an anchoring root portion secured in the periphery of the wheel and aheat transfer portion extending radially inward from the anchoring rootportion across the cooling space, said vane portion having alongitudinally extending recess communicating through the root portionwith the hollow interior of the heat transfer portion, a coolant in saidrecess adapted to transfer heat from the vane to the heat transferportion, said coolant decreasing in density with an increase intemperature whereby hot working fluid acting on said vane portion todrive the turbine will decrease the density of the coolant in the vaneportion whereupon rotation of the turbine will centrifugally dischargeheavier cool coolant from the cooling portion of the blade into the vaneportion for replacing the heated coolant to create a flow of coolantalong the length of the blade, and means for flowing a cooling mediumthrough the cooling space of said turbine for conducting heat from theheat transfer portion of the blade in the cooling space.

8. A turbine wheel assembly comprising a wheel having blade anchoringmeans around the periphery thereof, a plurality of turbine blades havingroot portions anchored in said blade anchoring means, vane portionsextending radially outward from said root portions and heat transferportions extending radially inward from said root portions, said bladesbeing hollow and each having a cavity extending from the heat transferportion through the root portion into the vane portion, said wheelhaving a cooling space inwardly from the periphery, said heat transferportion of the blades extending across said cooling space, means forcirculating a cooling fluid through said space to flow around said heattransfer portions of said blade to dissipate heat therefrom, and acoolant in the cavity of each blade adapted to decrease in density withan increase in temperature to establish a circulation of heated coolantfrom the vane portion to the heat transfer portion as the wheel assemblyis rotated.

9. A turbine and blade assembly for a gas turbine engine required to runat high temperatures which comprises a turbine wheel having a rimportion adapted to anchor a plurality of turbine blades and a heattransfer chamber inwardly from said rim portion, hollow turbine bladesdisposed radially around the periphery of said wheel and. havinganchoring roots secured in said rim portion, vanes extending radiallybeyond the rim portion and heat transfer portions extending radiallyinwardly from the root portion into said cooling space, each bladehaving a continuous cavity extending from the heat transfer portionthrough the root portion into the vane portion, a coolant medium in thecavity of each blade adapted to set up a convective current when thevane portions of the blades are heated by working fluid and when theturbine is rotated whereby the vanes will be cooled by the coolant andthe coolant will be cooled by the heat transfer portions of the blades.

10. A turbine comprising in combination, a wheel having two axiallyspaced flanges with outer peripheries defining a rim, a blade anchoredbetween said flanges and having a vane portion extending outwardly fromsaid rim defining outer peripheries of the flanges together with aninner portion extending radially inwardly from said outer peripheries ofsaid, flanges into the space between said flanges, said blade beinghollow and having a continuous cavity extending through the vane portionto the inner portion thereof, means for circulating a first coolingmedium through the space between the flanges inwardly from said outerperipheries of the flanges and around said inner portion of the blade indirectcontact therewith, and a second cooling medium having decreaseddensity with increased temperature contained in said cavity whereby the,heating of said second cooling medium bythe vane portion of the bladewill decrease the density of said second medium in the vane portionwhile rotation of the Wheel will displace the thus heated second mediumwith cooled and hence heavier portions of said second medium from theinner portion of the blade for setting up flow of the second medium totransfer heat from the blade to the first cooling medium circulatingaround the inner portion of the blade.

References Cited in the file of this patent UNITED STATES PATENTS1,114,564 Winkler Oct. 20, 1914 1,306,470 Dady June 10, 1919 1,501,862Midgley July 15, 1924 1,938,686 Brooke Dec. 12, 1933 2,256,479 HolzwarthSept. 23, 1941 2,292,072 Hanna Aug. 4, 1942 2,369,795 Planiol Feb. 20,1945 2,407,164 Kimball Sept. 3, 1946 FOREIGN PATENTS 229,933 SwitzerlandFeb. 16, 1944 491,738 Germany Feb. 12, 1930 665,762 Germany Oct. 3, 1948907,059 France June 11, 1945

